Well, I always like seeing how other people envision some of the classics that don't have a "canon" appearance- 682, SCP-040, SCP-939… makes for a cool comparison sometimes.

If you're looking to practice and challenge your skills, go digging for ones that you haven't seen used a lot in tales. My favorites out of the ones that I have painted/have on my to-do list are ones with a really strong atmosphere and written imagery to play off of. Ones with lots of specific details are a fun way to practice as well if you're at all interested in the process of concept art and/or illustration- use the description like a spec sheet, and try to match what you think the original author had in mind. Having a list of traits to follow often breaks you out of your "default" standards, and pushes you to be more creative with parts you'd normally ignore.